Bifurcated Halogen Bonding Involving Diaryliodonium Cations as Iodine(III)-Based Double-σ-Hole Donors

Abstract

Three diaryliodonium tetrachloroaurates(III), [Ar1IAr2][AuCl4] (Ar1/Ar2 = Ph/Ph (1), Ph/Mes (2), o-(C6H4)2 (3)), were obtained as solids (62-80%) by the metathetical reaction of [Ar1IAr2](CF3CO2) and H[AuCl4]. In particular, the single-crystal X-ray diffraction studies of 1-3 revealed three-center bifurcated C-I···(Cl-Au-Cl) halogen bond (XB) and the more conventional interionic two-center C-I···Cl-Au XB. An XB with the iodine(III) center of a diaryliodonium cation can be formed even when ∠(C-I···X) is much less than 180° (decrease by 55° in our experiments). A Cambridge Structural Database search and processing revealed other examples of bifurcated XBs involving diaryliodonium species. All recognized bifurcated XBs with diaryliodonium cations were classified and divided into two categories: "bifurcated plus two-center"and "double-bifurcated"structural types. The nature and energies of the XB interactions were studied by density functional theory (DFT) calculations and a topological analysis of the electron density distribution in the framework of the quantum theory of atoms in molecules (QTAIM) at the ωB97XD/DZP-DKH level of theory. The nature of all XB contacts is purely noncovalent, and the total energy of bifurcated XBs is generally ca. 50% higher than the energy of two-center XBs.